no need to send the encrypted block twice

src/main/java/ch/fhnw/kry/CTR.java

@@ -40,13 +40,12 @@ public class CTR {
      *
      * @param block Encrypted block (only lower 16 bits get looked at).
      * @param idx   Block index.
-     * @param y     Y at index idx.
      * @return Decrypted block (in the lower 16 bits of the int).
      */
-    public int decrypt(int block, int idx, int y) {
+    public int decrypt(int block, int idx) {
         int e = (iv + idx) % (1 << BLOCK_LENGTH); // iv + i mod 2^16
         e = spn.encryptBlock(key, e); // yes, we need the encryption function, as this is CTR
 
-        return y ^ e;
+        return block ^ e;
     }
 }